Abstract
1. Rrce vaneties of varlous distncts of Eastern Asia, 163 in total number (same to those used in the preceding works), were seeded repeatedly throughout a year at the interval of 30 to 50 days, and the relation between the date of heading and the days of growth period (frong seeding) was investigated on each variety. The same experiment was repeated three times in 1945, 1946-', 47' and 1948-'49. 2. For measuring the sensibility to day-length, the ratio of shortening of growth period to an unit shortening of day-length at the time of flower bud formation (assumed as 30 days before the heading) was calculated on each variety. This ratio varied in a same variety with the day-length ; the daylength at which the ratio was largest was regarded as the "critical day-length" (for the most radical change of growth period), and the sensibility to day-length was expressed in terms of the arc tangent of the largest ratio (named as T.D.M. ).
